It is well known that the application of cellulase to cotton fabrics results in the unwanted destruction and weakening of cellulosic fibers. The natural propensity of cellulase to hydrolize cellulose can easily cause cellulose to leave entire regions of fabric weakened, altered and undesirable for use. Hydrolysis of cellulose by cellulase also forms sugars which have the potential of yellowing when exposed to heat during drying.
Consequently, previous inventors have found limited ways of applying cellulase to cellulosic fibers. Japanese Patent No. Sho S2-48236, for instance, immerses a fabric in a batch process where an enzyme solution is recirculated for a short time. The process imparts mild, hygroscopic properties and smoothness to a fabric. Applying cellulase in such manner, however, weakens the fabrics from 15% to 50%. Japanese Patent No. Sho 58-54082, Kurashiki pretreats a fabric with a swelling agent, neutralizing the fabric before applying cellulase. The swelling agent, imparting strength to the fabric, nevertheless appreciably weakens the fabric. U.S. Pat. No. 4,343,070 Wade teaches the use of cellulase applied with a wetting agent for short periods of time in order to remove lint from cotton seed. The cellulase is applied "subjectively" however, and the patent does not teach any conditions which will delint fabrics without undesirable strength loss.
U.S. Pat. No. 4,822,864 (Olson), by contrast, teaches use of a batch process where clothing is intentionally damaged with cellulase during application. The fabric is contacted with the cellulase solution and agitated, and the cellulase enzyme cleaves cellulose from the surface of the fabric and indigo dye to give a stone washed look. The process is used to modify denim where such a "stone washed" look is often desired.
As the use of open end yarn has increased, the need to modify cellulosic fabrics without the destruction, discoloration and weakening of fibers has also increased. For years, most cotton-comprising fabric was produced using ring spun yarn, a high quality yarn which is tightly twisted with little fraying of individual fibers. Open end spinning technology, however, has enabled manufacturers to use less expensive, lower grades of cotton to develop open end yarn. Today, only the finest garments are made from ring spun yarn.
The increased use of fabrics made from open end yarn, particularly cotton towels, has demonstrated that open end fabrics lint substantially more than ring spun fabrics. Unlike ring spun yarn, open end yarn contains an appreciable number of protruding fibrils, or embedded lint precursors. Ordinarily, these embedded lint precursors remain with the open end yarn after the manufacturing of a cotton fabric. During the first wash, however, these precursors break free, entangle, and form lint.
Accordingly, "embedded lint precursors" as is used herein, means those fibrils that exist in the yarn, which when broken off, form lint. "Lint" as is used herein, means the entanglement of lint precursors ordinarily occuring at the first wash. "Delinting" means a process of removing embedded lint precursors with cellulase during the manufacturing process.
The embedded lint precursors are not the only fibrils that break free from an open end fabric. "Pilling" for instance, ordinarily refers to fibrils that are surface entangled during the repeated wear and washing of a fabric. Pilling, however, results from the entanglement of ingrained non-protruding cellulosic fibrils that resist being removed during the first wash, not the protruding embedded cellulosic fibrils. Similarly, entire cotton fibers may break free from a fabric by the effect of a swelling agent or repeated use. Such removed cotton fibers, however, are not the removed protruding lint precursors that are refered herein as lint.
The customary ways of applying cellulase to cellulosic fibers have prevented consumers from enjoying towels that do not exhibit an appreciable amount of lint after a first washing. Manufacturers, receiving numerous complaints from consumers about the appearance of lint on cotton towels when the towels are first washed by a consumer, have used prior methods in vain trying to delint fabrics effectively. The use of a swelling agent, although reducing strength loss, nonetheless produces undesirably weak fibrils and inadequately removes embedded lint precursors. Similarly, the application of cellulase to a fabric that is agitated and circulated to produce a "stone wash" appearance, destroys desired fibrils in fabrics that are not ordinarily stone washed and can give increased amounts of lint and excessive strength loss.
It has now been discovered, contrary to ordinary custom and usage, that cellulase may be applied, during a continuous manufacturing process, to selectively remove embedded lint precursors without causing the fabric to lose an appreciable amount of strength. It has further been discovered that cellulase may be applied without pretreating the cotton fabric with a swelling agent.
It is the principal objective of this invention to selectively digest unwanted fibrils that form embedded lint precursors in cotton fabrics while obtaining a strength loss of less than 10%. It is another objective of the invention to remove embedded lint precursors from cotton fabrics without creating an unaccepatable yellowing.